Im Having Problems With My Girlfriend, She Acuse Me Of

Im having problems with my girlfriend, she acuse me of cheating, constanly and that she see me with another woman and is not true and she believe it. I cant go no where cuz she always fighthing with things I don't do, im 65years , she is 43, I want she go to see a doctor and she said nothing is wrong with her, im taking her this week to look for help, what kind of doctor should I look for? please, help me